Hydroponics, which does not use soil, has conventionally been used. Hydroponics supplies nutrition to a plant by soaking the roots as part of the underground portion in nutrient solution. In this case, the surrounding temperature of each of the aboveground portion and the underground portion is controlled independently. For example, as disclosed in Patent Literature 1, temperature is controlled depending on the characteristic of the plant such that the ambient temperature around the underground portion is lower than the ambient temperature around the aboveground portion.